This invention relates to the continuous production of a polymeric expandable foam bun through an open top conveying apparatus which allows the foam to rise freely due to chemical reaction until full height is obtained. The bun is then cured and subsequently is subjected to a transverse sawing operation to saw the continuous bun into relatively long (25-200 feet) lengths which can be more easily handled and processed. The typical foam bun will have a cross-sectional width of approximately 81 inches and a height that varies from 25-40 inches.
After the bun is cross-sawed into even shorter lengths, it is then subjected to a further sawing operation, along a horizontal plane transverse to the height dimension, in which the foam is cut into slabs of the proper thickness for mattresses and cushions. Since different manufacturers require different thicknesses, it is desirable to vary the bun height somewhat, so that the total height will equal, as nearly as possible, an even multiple of the individual slab thickness to minimize waste.
A problem exists in varying overall bun height, to any appreciable extent, at a given pouring rate. Previous methods that have been attempted include the device shown in the Ferstenberg U.S. Pat. No. 3,672,348, which is illustrative of a device which controls the upper contour of the foamed bun (bun height) by varying the lateral pressure and the inclination of the conveyor type molding apparatus onto which the reactants are initially poured. Such an apparatus, while technically feasible, is both expensive to build; difficult to maintain in satisfactory operation condition because of the many parts which move relative to each other; and not easily altered to change the bun height. Further, according to the Ferstenberg disclosure, when the bun height is changed, the width is also changed, which is not satisfactory for the production of foam buns having a constant width, and variable height.
Some alteration in bun height can be made by varying the conveyor speed, which is generally easily changed, however, only minor variations can be made without deleteriously affecting the quality of the foam bun output. If the conveyor is too slow, the foam material backs up at the outset in front of the creamline, which is called "undercutting," and results in a bad quality foam. On the other hand, if the conveyor speed is too fast, the cell structure of the foam will become non-uniform, which is also undesirable. Therefore, with a constant pour rate, pour angle, and creamline height, the conveyor speed must remain fairly constant and cannot be significantly varied to achieve desired variances in bun height.
Another possibility might be to vary the conveyor speed and the pour rate, which one might think would overcome the problems set forth in the paragraph above. However, changing the pour rate can also directly cause considerable difficulty and lead indirectly to other problems. When the pour rate is changed, absent other adjustments which may be difficult or practically impossible with such types of conveyors, the creamline will tend to vary longitudinally with respect to the conveyor bed, thus varying the point at which the bun attains full height. It is apparent that this is not satisfactory.
From the above discussion it is easily seen that the problem is more difficult than may at first appear, and it is desirable to arrive at some solution where the bun height may be selectively varied through a significant range with a minimum of adjustments necessary to the system as a whole.